Gold or steel nib — what does gold actually buy?

Spring, not smoothness. Gold’s lower stiffness gives a cushioned, slightly bouncy stroke and (in some designs) mild line variation. Smoothness comes from the tipping polish, and excellent steel nibs — TWSBI, Lamy, Jowo — are polished as well as most golds.

Buy gold for the feel and the occasion around $150+; buy steel to get 95% of the writing experience for a fifth of the money. Nobody reading your handwriting can tell which you used.